/Engine/Source/Runtime/GeometryCore/Public/Util/IteratorUtil.h
SeeFDynamicMesh3::VtxTrianglesItrfor an example
template<typename OutputType, typename InputType, typename InputIteratorT> class ExpandIterator
InputIteratorT
Cur
int
CurExpandI
OutputType
CurValue
InputIteratorT
End
ExpandFunctionT
ExpandFunc